Levosimendan, which is the (−)-enantiomer of [[4-(1,4,5,6-tetrahydro-4-methyl-6-oxo-3-pyridazinyl) phenyl]hydrazono]propanedinitrile, and methods for its preparation are described in EP 565546 B1 and WO 97/35841. Levosimendan is potent in the treatment of heart failure and has significant calcium dependent binding to troponin. Levosimendan is represented by the formula: 
The hemodynamic effects of levosimendan in man are described in Sundberg, S. et al., Am. J. Cardiol., 1995; 75: 1061 −1066. Pharmacokinetics of levosimendan in man after i.v. and oral dosing is described in Sandell, E.-P. et al., J. Cardiovasc. Pharmacol., 26(Suppl.1), S57-S62, 1995. The use of levosimendan in the treatment of myocardial ischemia is described in WO 93/21921. Transdermal compositions of levosimendan are described in WO 98/01111. Clinical studies have confirmed the beneficial effects of levosimendan in heart failure patients.
Administration of a drug by parenteral, e.g. intravenous, administration provides a number of advantages including the following:                an almost immediate response may be obtained by administering by intravenous injection or infusion a solution, usually aqueous, of the drug;        the therapeutic response may be more readily controlled by administering the drug parenterally; and        a drug can be administered parenterally to a patient when it cannot be administered orally because of the unconscious state of the patient, or because of inactivation or lack of absorption in the intestinal tract.        
The manufacture of levosimendan solutions, and particularly solutions suitable for intravenous use, involves a number of problems which are caused by the sensitivity of levosimendan against chemical and physical influences. In solutions levosimendan is sensitive to chemical degradation which limits the shelf-life of solutions and may produce undesirable degradation products. Levosimendan is also poorly soluble in water and precipitates easily from aqueous solutions. The precipitation of intravenous solutions is extremely dangerous because particulate material may occlude the blood vessels. The solubility of levosimendan decreases further strongly when the pH is lowered from neutral, so that low pH would in principle seem unfavourable. Thus, there is a need for improved aqueous formulations of levosimendan which are chemically and physically stable under prolonged storage and suitable for intravenous administration.